The present study aimed to evaluate the hydrogen production of a microbial consortium using different concentrations of sugarcane vinasse (2-12 g COD L-1) at 37 degrees C and 55 degrees C. In mesophilic tests, the increase in vinasse concentration did not significantly impact the hydrogen yield (HY) (from 1.72 to 2.23 mmol H-2 g(-1) CODinfluent) but had a positive effect on the hydrogen production potential (P) and hydrogen production rate (R-m). On the other hand, the increase in the substrate concentration caused a drop in HY from 2.31 to 0.44 mmol H-2 g(-1) CODinfluent in the tests performed at 55 degrees C with vinasse concentrations from 2 to 12 g COD L-1. The mesophilic community was composed of different species within the Clostridium genus, and the thermophilic community was dominated by organisms affiliated with the Thermoanaerobacter genus. Not all isolates affiliated with the Clostridium genus contributed to a high HY, as the homoacetogenic pathway can occur. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.